Lightweight unit



June 16, 1936. G. B. BROWN 2,043,988

LIGHTWEIGHT UNIT Filed Feb. 28, 1955 INVENToR George Brown QM/maATTORNEY Patented June 16, 1936 UNITED STATES PATENT 4OFFICELrGn'rwEIGH'r UNIT George B. Brown,

J ohns-Manville Somerville, N. J., assignor to Corporation, New York, N.Y.,

11 Claims.

This invention relates toa lightweight unit, particularly a preformedacoustical unit.

' It is an object of the invention to provide an inexpensive buteil'ective, lightweight sound-absorbing or thermal-.insulating unitcomprising central and edge portions coacting to increase the strengthand rigidity while preserving the overall low density, adaptability, andother desirable properties of the unit, including the appearancethereof. Other objects and advantages will appear as the description ofthe invention progresses.

Brieily stated, the preferred embodiment of the invention` comprises an'acoustical unit including a central or body portion of spaced sheets,that are per se relatively ineffective in sound-absorption and thatdefine between them a labyrinth of discontinuously communicating spaces,and rigid edge sealing and reenforcing elements adhered to the centralportion, the said edge and centralportions being constructed preferablyof the same materials, whereby they are adapted toreact identicallyunder changing conditions of environment. The invention comprises, also,a unit o1' the type described in which the edge sealing elements andalso an element applied to the back thereof are sound-impermeable andadapted to minimize the passage of sound and the circulation of airthrough the edges and back of the unit. Further, the invention comprisesan acoustical element including sound-absorbing spaces and parallel,closely spaced, narrow slits connecting the said spaces with each otherand with an exterior surface of the element.

'I'he invention is illustrated in the drawing in which:

Fig. l shows a plan view ci acoustical unit, which is in part brokendown to show the inner structure of the unit;

Fig. 2 shows an edge view of the unit illustrated in Fig. l;

Fig. 3 shows a cross sectional view on line 3-3 of Fig. l;

Fig. 4 shows a plan View, in part broken away, ci a modiiled form ofcentral portion lor soundabsorbing. element; and

Fig. 5 is a cross sectional Fig. 4.

lin the various figures like denote like parte.

The drawing shows a preformed lightweight unit, particularly adapted forthe absorption of sound, comprising a sound-absorbing elementconstituting the central portion i, and edge seaiing and reeniorcingv.strips or elements 2, in-

of a preferred type T@leur on line 5--5 of reference characters tegrallyunited, as by sodium silicate adhesive, to the said central portion. Theunit is provided with a sound-permeable outer sheet 3, which is really apart of the sound-absorbing structure, but may be herein referred to,for convenience, as the facing element. Also, the unit is provided, atits back, with an outer backing sheet 4 that is preferablysound-impermeable.

The central or body portion l comprises, suitably, composited sheetsthat are in themselves relatively ineiective in sound-absorption butdene sound-absorbing spaces or passages 5. The .composite includessheets 6 of irregular surface, alternated with sheets 'I of planesurface. 'Ihe sheets of irregular surface may be corrugated and arrangedin the assembly with the corrugations in one sheet extending at anangle, say crosswise, to the corrugations in adjacent sheets. Thecomposited alternating sheets of plane and irregular surface areprovided with perforatlons or openings 8, spaced suiiiciently closely toadmit incident sound and providing lateral communication between thespaces defined between the sheets.. The perforations in adjacent sheetsof the same type of surface may be non-registering. This provision,together with the crossing of thecorrugations in adjacent corrugatedsheets, provides for maximum discontinuity of communication between thespaces, and causes sound within the unit to undergo numerous deilectionsin paths that may be of great length as compared to the wave length ofthe sound itself.

In the modification shown in Figs. 4 and 5, the openings adapted toadmit incident sound are long slits, say saw kerfs 9. In the individuallayers, consisting each of a sheet of plane surface and a corrugatedsheet adhered thereto, the saw kerfs extend through the sheet of planesurface, to divide it into a plurality of narrow parallel bands, andextend also through the tops of the corrugations on one side of theseveral corrugated sheets, to cause the numerous spaces defined by thetroughs in the corrugated sheet and the plane sheet to communicate witheach other.

The central portions are relatively compressihle and non-rigid and haveinadequate strength for many purposes. Furthermore, the edges thereof,if the central portion were used alone as an acoustical unit, wouldpresent va more or less uneven or ragged appearance and `would provideno dem, strong area for nailinrar or similarly securing to a supportingsubstructure. These disadvantages vare overcome by the edge portions 2.These portions are rigid, preferably impermeable to sound, andintegrally united to the central portion on the edges thereof. The

edge portions establish the thickness of the unit,`

-ous felted fibers of the type of asbestos. Thus,'

the central portion may be composed largely of asbestos paper. Suchpaper contains usually a small proportion of a binder, such as starch,and of cellulosic fibers such as newsprint, say in the proportion of 20parts by weight of the newsprint to parts of asbestos. The asbestospaper may be thin, weighing, for example, 5 pounds per hundred squarefeet of the paper. The paper may be provided with irregularities ofsurface, such as corrugations or indentations, in conventional manner.

The sheets comprising the backing and also the facing element may beconstructed of the same material as the paper described. These outersheets, however, are conveniently made somewhat thicker than the sheetswithin the central portion, say twice as thick, in-order to assist inmaintaining the dimensions of the finished unit. 'I'he facing element oftype described is sufficiently stiif and strong to be shape-retaining,yet is substantially non-vibratile under the influence of incidentsound.

The edge sealing and reenforcing elements also are made preferably ofthe same materials as the central portion, in order that the centralportion and the edge sealing members may show the same behavior underchanging conditions, such as uniform expansion and contraction withchanges in atmospheric humidity. The edge sealing strips may consist ofasbestos fibers in the form of millboard. For a unit that is 16 inchessquare by 1 inch thick, the edge sealing strips may be 1 inch wide fromfront to back-and I/ Vinch thick. They are suitably joinedat their ends,as in the tongue and groove joint illustrated at I0.

The facing element 3 may consist of sheet material of irregular surface,including imperforate, that is, sound-impermeable elevated portions Hand portions I2 that are depressed with respect to the elevated portionsand that contain openins adapted to admit incident sound. In the formillustrated, the facing element has the appearance of a modified basketweave structure, with the cross strips omitted, and is provided withslits I3, in the areas intermediate the tops of the elevated portionsand the bottoms of the depressed portions.

In making an acoustical unit of the type described, there are firstprovided the component materials such as sheets of plane-surfacedasbestos paper and corrugated asbestos paper, asbestos millboard', andthe adhesive that it is desired to use in compositing the various parts.These parts may be put together in convenient manner, as, for example,by hand or by machine.

The sheets of paper that are to constitute the central portion are cutto desired size, say 151A x 151A inches. The tops of the corrugations inthe corrugated paper are provided with a coating of sodium silicatesolution as the adhesive, and there are then formed a number ofcomposites consisting of sheets of plane surface and corrugated surface,of one-ply thickness of each kind of paper. These composited one-plysheets provided, they may appropriate surfaces of the partially formedunit 7`5- are then passed over a pin roll, while being pressedthereagainst, and thus provided with perforations closely spaced andadapted to admit incident sound. For example, the sheets may be pressedagainst a roller carrying closely spaced piercing pins, say 1%; inchapart. Preferably the sheet of plane surface is nearest to the rollerduring the perforating operation, so that the pins l pierce holescompletely through the plane sheet and partly through the adjacentcorrugated 10 sheet, particularly through the elevated portions of thecorrugated sheet adjacent to the plane sheet.

If the central unit is to be of the type illustrated `in Figs. 4 and 5,one-ply sheets of the type de- 15 scribed, but not perforated, arepassed under a gang of closely spaced rotating saws, as, for eX-. ample,saws adapted to cut kerfs nl; inch wide and inch apart. The composite ispassed through with the sheet of plane surface turned 2o towards thesaws, and the spacing on the sheets with respect to the saws is suchthat the saw kerfs extend through the plane sheet and divide it into aseries of narrow parallel bands but extend only sufficiently far intothe corrugated 25 sheet to saw through the tops of the corrugationsadjacent to the plane sheet.

One-ply composite sheets; provided with the sound-permeable openings asdescribed above, are then assembled and adhered together, intoa centralor body portion of desired thickness, say 1 inch. The adhering iseffected by means of adhesive, of type described, applied over the highspots of the corrugations in the several composites of one-plythickness.

Acentral or body portion so made is then united to the edge elements 2.These elements are provided in proper length and'with tongues or groovesat their ends. The edges of the central portion are rst heavily coatedwith an aque- 40 ous solution of sodium silicate or the like. The edgeelements 2 are then oriented properly and forced against the silicatededges of the central portion, to give a firm bond therewith and also tocause the ends of the said edge elements to 45 be joined with eachother, as illustrated in the figures. 'I'his may be done by hand or by adevice commonly known as a ,bulldozer. During thisl uniting of the edgesto the central portion, distortion of the relatively weak centralportion is 50 avoided by rigid plates disposed both above and below thecentral portion and maintained in position, to prevent bulging of thecentral portion during the pressing of the strips against the edgesthereof. 55

The central portion with the adhered edges is then provided with thebacking and facing sheets. As stated, the backing sheet is suitablyimperforate asbestos paper of plane surface and the facing element' is asheet having the appearance 60 of a modified basket weave, with slits inthe areas intermediate the elevated and depressed portions. The facingelement may be yieldable and is made in any convenient manner, as byproviding a sheet of asbestos paper with discontinuous, parallel slitsand then elevating areas between certain of the slits and depressing theadjacent areas. This may be done by passage of the sheet betweencoacting rollers, having on their surfaces meshing elevations anddepressions and means 70 for cutting slits in the areas intermediate thesaid elevations and depressions. When the facing and backing sheets havebeen be applied by hand to the staggered, G5V

backing sheets are first formed in long lengths.I and are drawn betweenspaced rollers, so that the facing sheet rideson one roller and thebacking sheet on the other and there is left between the sheetsfspacefor feeding therein the incomplete unit comprising the central portionand ad-- hered edge strips. Adhesive is applied to theA inner side'ofthe backing sheet and to the backs of the depressed portions of thefacing sheet before the sheets are passed over the said rollers.

Between the rollers the sheets are pressed against the proper surfacesof the unit and are adhered thereto.

After passage of the assembly from the rollers it is trimmed roughly, asby cutting the facing and backing sheets approximately at the edges ofthe unit. v

The unit with adhered facing and backing sheets is then subjected to anvoperation to establish approximately uniform thickness thereof, and tosetv the unit in final shape and size. Thus, the unit may be compressedbetween steamheated plates maintained at selected distances apart in ahydraulic press and held therein until the moisture present in the unit,including water added with the adhesive, is removed by evaporation.

During this operation the edge strips, which are relativelyincompressible as compared to the easily crushed central portion, inconnection with the spacing of the plates in the press, establish thethickness of .the final unit.

When it is desired to have a facing element more stiff and rigid than isasbestos paper, the facingelement of the'drid unit may be sprayed orpainted over-its surface with a solution of shellac, a phenol-aldehydeproduct (bakelite) or other suitable stiiening agent.

The thus finished surface is then again dried. Finally, the unit issized and/or provided with beveled edges as illustrated. For this theremay be used cutting wheels of carborundum or the like. f

Since the equipment used in the various steps of the manufacture is nota part of the invention,

it is considered unnecessary to illustrate it.

Units made as described, in 1inch thickness, have been found to absorb50 to 65% of incident sound of a frequency of 512 cycles per second.

When it is desired to construct such a unit for use as thermalinsulation, the procedure outlined may be followed with the exceptionthat lthe perforations, slits or other sound-permeable openings areomitted from the structure.

Likewise, the `backing or facing elements may be omitted if theirfunctions are not desired. lThe facing element, along with otherfunctions, adds to the desirable appearance of the unitand provides asurface that may be pmnted, as by spraying or brushing, without closingthe slits or openings disposed rearwardly with respect to the tops ofthe elevated portions.

The details, that have been given are for the purpose of illustrationand not restriction. Variations within the scope of the appended claimsmay be made without departing from the spirit and scope of theinvention.

What -I claim is:

1. An acoustical unit comprising a sound-permeable face, a compressible,sound-absorbing central portion, provided with sound-absorbing spacescommunication laterally with each other and with openings communicatingwith the face of the unit .and adapted to admit incident sound, andrigid, relatively non-compressible, edge portions united to andenclosing the central por- 5 tion at the edges thereof, the said centraland edge portions being constructed of the'same materials, whereby theyare adapted to contract and expand in unison under changing conditionsof atmospheric humidity.

2.l An acoustical unit comprising a compress` ible sound-absorbingcentral portion, including a plurality of sheets that are relativelyineffective per se in sound absorption, define sound-absorbing spacesbetweenthe sheets; and are provided with openings adapted to admitincident sound, rigid, relatively non-compressible, sound-impermeableedge portions united to and enclosing the central portion at the edgesthereof, whereby thev thickness of the unit is established and thepassage of sound through the edges of the unit is minimized, a yieldablesound-permeable facing sheet extending over and united to the faces ofthe said central and edge portions, and a soundimpermeable backing sheetextending over and united to the back of the said unit.

3. An acoustical unit comprising a compressible sound-absorbing centralportion, including a plurality of porous sheets of felted fibrousmaterial, that a-re relatively ineffective per se in lsound absorption,define sound-absorbing spaces between the sheets, and are provided withopenings adapted to admit incident sound, and rigid, relativelynon-compressible, sound-impermeable edge portions united to an enclosingthe central 35 portion at the edges thereof, the said edge portionsbeing constructed of the same kind of felted fibrous material as thecentral portion, whereby similar behavior of the two portions underchanging conditions of environment is obtained. 4,0 4. An acousticalunit as described in claim 2 including an outer sheet extending over andunited to the faces of the central and edge portions of the unit, thesaid outer sheet. having irregulariyties of surface including elevatedportions and portions depressed with respect to the elevated portionsand being provided in the lsaid depressed portions with openings adaptedto admit incident sound. 4

5. An acoustical unit as described in claim 3 50 comprising a substanceof negative capillarity for water, adapted to minimize the absorption ofwater vapor, impregnated in limited proportion into the said fibrousmaterial, whereby the porosity of the fibrous material is preserved andthe tendency thereof to absorb Water-vapor is reduced: f

`6. A preformed acoustical unit comprising a face portion, edge stripsof asbestos millboard and aA central portion united to the edge stripsand bounded thereby and including, in the said central portion, aplurality of composited sheets of alternating plane-surfaced andirregularly surfaced asbestos ;paper,` defining therebetweensound-absorbing spaces communicating laterally with each other, andbeing provided with openings communicating with the face of the unit andadapted to admit yincident sound.

'7.'A preformed acoustical unit comprising a face portion, edge stripsof asbestos millboard and a central portion united to the edge stripsand bounded thereby and including, in the said sound-absorbing spacescommunicating laterally with each other, and being provided withopenings communicating with the face of the unit and adapted to admitincident sound, the openings in the several sheets of any one kind ofsurface being in non-registering relationship.

8. A preformed acoustical unit comprising a face portion, edge strips ofasbestos millboard and a central portion united to the edge strips andbounded thereby and including, in the said central portion, a pluralityof composited sheets of alternating plane-surfaced and corrugatedasbestos paper, defining therebetween sound-absorbing spacescommunicating laterally with each and bounded thereby and including, inthe said central portion, a plurality of composited sheets ofalternating plane-surfaced and corrugated asbestos paper, deningtherebetween soundabsorbing spaces communicating laterally with eachother and being provided with opening communieating with ther face ofthe unit and adapted to admit incident sound, the corrugations in theseveral sheets being arranged crosswise with respect to the corrugationsin adjacent sheets.

10. An acoustical unit as described in claim 6 including a facingelement of asbestos paper forming the outer. sheet of thesound-absorbing element, the facing sheet having imperforate forwardportions and portions disposed rearwardly with respect to the forwardportions and provided in the said rearwardly disposed portions withopenings adapted to admit incident sound.

1l, An acoustical unit as described in claim 6 including an imperforatebacking element of as bestos paper adhered to the back of the unit and afacing element of asbestos paper forming the outer forward sheet of thesound-absorbing ele ment, the facing sheet having the appearance of amodied basket weave, having imperforate forward portions and portionsdisposed rearwardly with respect to the forward portions, provided inthe said rearwardly disposed portions with openings adapted to admitincident sound, and having a stiffening material applied to the facingsheet with preservation of the said openings.

GEORGE B. BROWN.

